beg borrow or steal
by airbefore
Summary: It's not her first time doing this and judging by the way she can feel Castle staring, it won't be her last. *One Shot. Complete*


**Disclaimer:** All television shows, movies, books, and other copyrighted material referred to in this work, and the characters, settings, and events thereof, are the properties of their respective owners. As this work is an interpretation of the original material and not for-profit, it constitutes fair use. Reference to real persons, places, or events are made in a fictional context, and are not intended to be libelous, defamatory, or in any way factual.

**AN:** Fair warning, this fic is just a thinly veiled excuse to write a threesome for Beckett and Castle. If that's not your thing, go ahead and back out now, no hard feelings. Also, there is no plot to be found here so it _that's_ not your thing, again, bail now. If you're still with me, I hope you enjoy it. I've kinda driven myself half insane with this one.

* * *

This has to be a joke.

Beckett stalks toward her desk, coffee sloshing dangerously close to the rim of her mug. Castle slumps casually against the back of his chair, face relaxed and jovial as he laughs. The cup hits the wood with an overly loud thump drawing the attention of the woman perched on the edge, her long legs crossed and blond curls bouncing.

"Detective Beckett. So good to see you again."

Jerking her chair out, the wheel catching hard against the stiff plastic mat that she'd insisted on after the last time Castle and the boys left scuff marks on the floor with their illicit chair races, Beckett spins the seat and drops down, her arms crossed tightly over her chest. "Ms. Kaye," she nods, left foot twitching angrily against her right ankle. "To what do we own the pleasure?"

"Serena's in town investigating the theft of a painting from a private collection," Castle explains, excitement lacing his words. "She's working with Robbery."

"Which is on the third floor." Beckett flicks her gaze between Castle and Serena, the long dormant jealousy coming to life in her veins. "I'm sure Officer Vreeland would be happy to show you the way."

Serena slides off the edge of the desk, heels clicking against the floor as she straightens her skirt. "That won't be necessary, Detective. I just stopped by because I thought perhaps Rick might like to help with a little bit of undercover -" she smirks, amusement shining in her eyes - "since he was so convincing last time."

Castle makes eyes at her behind Serena, a plea forming on his lips. Holding back a sigh, she swivels her chair toward the desk and scoots forward, flipping open a thick file. "If you think he can help -" She waves her hand through the air dismissively before grabbing a highlighter, eyes never leaving the paper. "I'd be happy to get him out of my hair for awhile."

Castle lets out a squeak of indignation. "Hey -"

"Actually, Detective, I was hoping for your assistance as well."

"Oh?"

"For the setup to work, I need another woman."

"There are plenty of female officers in Robbery."

"Yes, there are. But let's be honest, none of them look like you." Beckett sits back and turns, finds both Serena and Castle scanning over her body, identical looks of appreciation on their faces. "I need someone who is both good at their job and hot. That's you."

* * *

Castle presses her into the wall, his warm hand sliding up the naked expanse of her thigh, mouth hot next to her ear. "I am _so_ glad you talked me into that biker role play last month." His fingers flirt with the hem of her skirt. "You are exceedingly hot in leather."

Beckett digs her fingers into his ass, tugging him closer and trying like hell to convince herself that it's only because she needs a clear line of sight into the dark recesses of the club. "You have to stop groping me, Castle. You're wrecking my concentration."

"Me groping you is pretty much the entire reason we're here," he murmurs, lips puckering at her jaw before trailing down her neck. "Kinda the point of a swingers club."

Arching away from the wall, she shifts, lifting herself off the thigh he's wedged between her legs. Desire burns hot in the pit of her stomach and Beckett fights the urge to sink down against him, to feel him pressed hard between her thighs. His mouth flits over the base of her throat and her eyes slam shut, hands convulsing on his shoulders.

"We're working," she hisses as his hands shift to her ass, broad palms gripping her tightly.

"I know."

"Then stop."

"He likes to watch." His teeth are sharp at her collarbone. "He wants a show and that's what we're going to give him."

The damp heat of his mouth seeps into her skin as his tongue, thick and wet, traces over the curve of her breast and she can feel him smile against her when the back of her head hits the cushioned wall with a muffled thump. "I cannot _believe_ I let you talk me into this."

"If I remember correctly, there wasn't a whole lot of talking involved." He rolls his body into her, hands sliding back to her hips, fingertips pressing hard into the fresh marks he left on her skin the night before. "Unless you consider begging a legitimate form of conversation."

Beckett tightens her fingers in his hair and yanks until Castle looks up at her, his lips shiny and tilted up into a smug grin. "I hate you," she hisses, leaning forward to bite at the corner of his mouth. Groaning, he presses her harder into the wall, hands roaming over her body, fisting into her scant clothing as he kisses her..

The feel of slim, cool fingers trailing along the side of her thigh brings her back to herself and she pulls away, her lips tingling. Looking to the right, she finds Serena standing close, watching. Leaning in, Serena presses her breasts against Castle's bicep, continuing to run her hand over Beckett's thigh. "He's not paying attention," she whispers."You're spending too much time on each other. You have to - "

Beckett feels Serena's fingers slide over hers on the back of Castle's head, twisting his neck toward her. Pressing up on her toes, she drags her mouth across his, red lipstick smearing between them. Castle goes stiff and jerks away, his eyes immediately flying to Beckett. "Kate -"

She slides her hand out from under Serena's, runs her fingers over his cheeks, an unexpected fire licking up her spine. Pressing her thumb to his chin, she nods and directs his head back toward the other woman.

Letting her hand her hands trail down to his chest, Beckett watches Castle lean toward Serena, meeting her lips tentatively. Her heart pounds as she lets her eyes roam, taking in the way his jaw flexes when he opens his mouth and lets his tongue come out, the graceful arc of Serena's neck as she strains up to meet him. Castle curls one arm around Serena's thin waist, pulling her body closer to them until Beckett can feel the heat of her pressing up against her side.

A low moan echoes between them, igniting a hot flash of _mine_ inside Beckett's chest. She burns with it as she grips Castle by the back of the head and pulls, separating his mouth from Serena's with a pop. He stares at her with wide eyes as she leans forward, her gaze flicking down to his open mouth. Just before she reaches him, Beckett turns, capturing Serena in a rough kiss. Her shoulder slams into Castle's chest as she wraps her hands around the other woman's arms, twisting them around until she has Serena's back pressed against the wall. Beckett blindly pushes her leg between Serena's parted legs, biting back a groan at the heat radiating against her thigh.

It's not her first time doing this and judging by the way she can feel Castle staring at them, it won't be her last.

Beckett's drags her hands over Serena's body, her stomach flipping as she encounters deep curves and smooth skin. Her hips pitch forward when two slim hands grip her ass, tugging her forward as she bares her teeth, biting hard at the other woman's bottom lip, a punishment for sins long past.

A deep groan rumbles in her chest when Castle's hands slips around her waist, his chest pressing against her back. The dual sensations - the hard wall of Castle behind and the soft give of Serena in front of her - set her hips rolling. Castle holds her tightly, the pressure of his palm against her abdomen the epicenter of the bone rattling shudder passing through her body.

"As much as we're all enjoying this," he husks, his voice low and full of gravel as he flicks his tongue into the hollow behind Beckett's ear, "I think our suspect just bolted."

Beckett slides out from between them, spinning around to scan the bar. A half-empty glass sweats onto the glass top of the table the suspect had been occupying the last time she checked. "Come on," she says, turning back around to Castle and Serena, the buzz of arousal still clouding her brain. "He can't have made it very far. Let's go."

Fuck.

* * *

"Are we going to talk about it?"

Castle walks up behind her in the breakroom. He doesn't touch her, just stands at her back, heat radiating off his body.

"Not here," Beckett answers, turning around to face him. She'd changed when they got back to the precinct, after handing both the suspect and the stolen painting off to the lead Robbery detective, but he's still in the clothes from club, shirttails untucked and hair mussed. He stares at her with hungry eyes and the arousal simmering in her chest boils up, spilling over the edges and burning through her veins.

"Kate -"

"Not. Here."

Castle follows her as she makes her way through the empty bullpen, stopping at her desk to pick up her bag, the leather skirt and tiny top tucked into the side pocket. He stays on her heels, his body nearly vibrating with energy and questions. They board the waiting elevator and Beckett pushes the button before leaning back against the side wall. Castle watches her with bright, curious eyes and she waves her hand at him, silently encouraging the words to flow.

"Go ahead. Ask."

Castle inhales deeply through his nose, lips pressed into a tight line. "I'm afraid that anything I ask is going to make me sound like either a pig or a voyeur."

"I'll let you know if it happens. Just ask me what you want to know."

"That wasn't your first time."

"That's a statement, not a question." She looks at the lit strip above the door, watches the numbers steadily decline. "But, yes. That wasn't my first time."

"Was it a college experimentation thing?"

"No."

Castle huffs as the bell dings, the doors sliding open. They step out into the nearly empty parking garage and head toward her car, tucked away in a dark corner.

"Come on, you gotta give me more than just 'no'."

"Don't ask closed ended questions."

"Beckett."

"It's really not an interesting story. I dated a woman briefly during my first year on the force."

Castle wraps his hand around her forearm, pulling them both to a stop, his head cocked to the side. "Define 'briefly'."

"Three months."

Nodding, he lets her go and resumes walking. "What happened?"

"She got a job offer in Florida. We broke up; it was amicable."

Beckett pops the trunk on the car and tosses in her bag, keys jangling in her hand as she slams the lid. Castle twists in his seat when she gets slides behind the wheel, his seatbelt already pulled across is his and cutting hard into his shoulder. "Have you been with women since then?"

"No."

"But you're still attracted to women? Because the way you were kissing Serena -"

"Yes, Castle, I'm attracted to women."

He hums as she starts the car and exits the garage, pointing them in the direction of her apartment. She needs to be loud tonight, to let herself scream and moan without the fear of disturbing sleeping family members. Castle's fingers swirl over her thigh and she feels her foot pressing a little harder on the gas pedal with each caress.

"Have you -" The question sticks to the back of her tongue. She's not nervous. Not really. They have a healthy and open sex life, having agreed early on to talk about and ask for the things they want. But the memory of the club, the feel of Serena's body under her hands - all soft and warm and deliciously feminine - is fresh in her mind and her stomach flips, anticipation filling her chest. "Have you ever been with two women? At once?"

"No," he answers without hesitation, his thumb swirling over her knee. "Had a couple of opportunities once upon a time but never followed through."

"Do you want to?" She casts a look at him from the corner of her eye, trying to gauge his reaction in the dim light of the car. The street lights flicker across his face and she thinks she catches just the slightest hint of a smile.

"Do _you_?"

Beckett sucks in a deep breath before letting her answer out in a relieved rush. "Yes." She holds the wheel steady with her left hand, dropping her right down to cover his on her thigh. "With you."

"Are you sure?"

"Yes."

Castle reaches into his pockets and pulls out his phone, holding it up for her to see. "Serena sent me a text when we were still at the precinct. She invited us to her hotel for 'celebratory drinks'."

The frame of the car shimmies slightly beneath them as they idle at a stop light. She looks over at him, smiling as the light turns green.

"Tell her we'll be there in ten."

* * *

The padded headboard is cool against her back as she watches them, fingers rubbing slow circles around her clit. Castle props himself up on his elbows and casts a long glance down his body at the blonde head bobbing between his legs before turning toward her with dark eyes. Leaning to one side, he extends an arm and Kate feels his fingers wrap around her ankle, tugging.

"Come here."

Rolling up to her knees, Kate cants her upper body over his, letting her bare breasts brush lightly over his chest when she drops down to kiss him. Castle reaches under her, dragging the backs of his fingers up the inside of her thigh. She groans when he pushes her hand out of the way and slides into her, his clever fingers curling in the way that he knows she loves. Kate pants into his grinning mouth as she rides his hand, her nails leaving angry red lines across his chest.

"I have told you lately that you're the best girlfriend ever?"

"Because you're currently having sex with two women and it was my idea?"

"Among other reasons."

Serena laughs and Kate turns her head, locking eyes with the other woman as she takes Castle into her mouth, her lips pulled tight. Castles fingers slip out of her as she trails kissing down his chest and abdomen, leaving a glistening trail in her wake. Twisting to face her, Kate lays a hand on Serena's shoulder stilling her movements.

"He likes this," she explains, leaning down to drag the flat of her tongue up the bottom of his shaft. Castle groans and grips her waist, head bouncing off the firm hotel mattress as his arms give out. Kate keeps her eyes open and fixed on Serena as she circles his base with her right hand and twists, lowering her mouth over him slowly. His hips buck off the bed and Serena grins, her hand coming to rest over Kate's.

"Let me try."

Lifting up, she watches Serena mimic her movements. A fresh wave of arousal crests low in her abdomen and she reaches out, her fingers scraping the damp curls off the other woman's cheek. Kate leans forward and runs her tongue along the seam where Serena's hand wraps around Castle, the salty tartness of skin bursting on her tongue.

"Oh my _god_."

Kate looks up, smiling at the wild look on Castle's face as he watches them, his stomach clenched and trembling. His eyes roll back when they run their tongues up the length of him in tandem, fingers curling tightly into the sheets. The deliciously slick heat of Serena's tongue next to hers sends sparks of need shooting down her spine and Kate turns her head, pressing her open mouth to the first patch of flesh she can find. Surging forward, she climbs over Castle's legs and pins Serena to the mattress, catching her mouth on the way down.

Making her way down Serena's body, nipping and licking, she feels Castle sliding out from under the tangle of limbs, the bed shaking as he shifts around. His hands grip her legs, spreading her knees apart as he tugs. Following his silent instructions, Kate tosses her right leg over his head and lowers herself down onto his waiting mouth. Castle groans and slaps her ass as she rocks over him, sliding against his tongue and chin.

Running her fingers through the deep crease of Serena's thighs, Kate lowers her head, filling her mouth with the sharp bite of arousal. Jaw aching with want, her tongue picks up a counterpoint to Castle's and Serena grips her hair, tossing her legs over Kate's shoulders as she grinds.

Heels dig into her spine and Kate moans, a dark need rising up in her chest. Pulling back, she grips Serena's hips, dragging her lips across her inner thigh. "Castle," Kate pants, pushing herself into his swirling tongue. Serena's hands twist into her hair, desperately trying to reconnect with her mouth, as Castle moans between her legs, his fingers digging into her ass. "Castle, stop. I want - _shit _- I want you inside me."

Even though she asked for it, she can't stop the whimper that creeps up her throat at the loss of his mouth. Her body sways with the bed as Castle flips over and clambers to his knees behind her. Strong hands tug her thighs further apart and Kate lifts her hips off the bed, her ribs hitching with a gasp as he pushes into her in one hard stroke. Pitching forward, she opens her mouth against Serena's rocking pelvis, lips and tongue working feverishly as Castle thrusts into her.

"Fuck, Kate," he groans, draping himself over her back, lips grazing her neck as he watches. "You're really into this, aren't you?"

It's all she can to moan and writhe as the sensory overload pulls her under. Slipping two fingers under her flicking tongue, she presses into the wet heat, pulling a velvet coated moan from Serena's lips. A heavy fog of bliss rolls across her mind, robbing her of any thought other than how amazing it feels to have Castle behind her and Serena under her, the combination of their grunts and moans driving her higher.

A high-pitched, feminine whine fills her ears and Kate twists her fingers, hips bucking uncontrollably as she feels Serena clamp down around her fingers, pulsing and tight. Serena's legs slip from her shoulders as she lifts off the bed and pulls Kate into a bruising kiss, nails digging hard into her back. Castle grits out a curse as his hips pick up speed, the wet smack of their skin echoing through the room. Sliding one hand up her back, Castle grabs a fistful of her hair and tugs, curving her spine into a concave arch as she comes hard and fast. He thrusts into her twice more and then follows her over, a garbled crush of words clogging his throat.

Kate collapses onto the bed, curling herself around the soft curves of Serena's body as she shakes with tiny aftershocks. Castle scoots up behind her, pressing a soft kiss to her shoulder blade before tugging at her hips, trying to pull her closer. She shrugs him off, body sated and comfortable, her skin the only thing keeping her from spreading across the bed in a puddle.

"I thought you didn't steal things that belong to other people?" Kate hears Castle ask the question, amusement in his voice as twines his fingers through hers, their joined hands resting on Serena's sweaty thigh. Normally she'd be annoyed at having no idea what he's talking about but in this moment, she truly could not care less.

"I don't." Serena's stomach shakes against her cheek as she chuckles and Kate closes her eyes, a soft smile playing on her lips at the feel of slim fingers running through her hair. "But I never said anything about borrowing."


End file.
